The etiological agents of autoimmune disease are endogenous lymphocytes which attack normal constituents of the individual. Autoimmune diseases share this common feature of being caused by the immune system's attacking the individual's own tissues. At the seat of all autoimmune diseases are the autoimmune lymphocytes which specifically recognize the individual's particular target antigens. Among the autoimmune diseases that are commonly recognized as such are rheumatoid arthritis, multiple sclerosis, some forms of diabetes mellitus, thyroiditis, myasthenia gravis, and anterior uveitis.
It has been found possible to grow, as long term cell lines, T-lymphocytes responsible for causing autoimmune diseases in laboratory animals. Among these diseases are encephalomyelitis, arthritis, and thyroiditis. Under certain conditions, these cells were found to be effective agents for vaccination against such specific autoimmune diseases. The lymphocytes were attenuated prior to injection so that they would not cause the autoimmune diseases. It was found that these vaccinations were quite effective in rendering the animals immune, or less sensitive (i.e., the disease was less severe) to such disease. Furthermore, when such animals which already showed symptoms of the disease were inoculated with these cells, the diseases were quite effectively treated.
As described by Cohen and Shinitsky, Proc. Natl. Acad. Sci. USA. 84:4577, 1987, and in parent application Ser. No. 910,876, T-cell vaccines against autoimmune diseases can be prepared by treating these T-cells with chemical cross-linkers, such as glutaraldehyde and formaldehyde. The membranes of these cells, treated with the cross-linking agents, were also effective as active ingredients of the vaccines. These compositions can also be used for alleviation of symptoms of these autoimmune diseases.
As a group, the psoralens, of which 8-MOP is a member, are compounds which have been found to cross-link molecules such as proteins very selectively under the influence of ultraviolet light, generally 320-400 nm in wavelength. These compounds, also known as furocoumarins, occur naturally in more than two dozen plant species. Two of the psoralen analogs, 8-methoxypsoralen and 4,5',8-trimethylpsoralen, are used clinically in the photochemotherapy of skin diseases such as psoriasis, mycosis fungoides, vitiligo, and eczema. Typically, patients are administered the psoralen orally or topically, and are then exposed to a measured dose of ultraviolet irradiation.
Recently, 8-methoxypsoralen, or 8-MOP, has been used to damage tumor cells circulating in the blood, Edelson et al., N. Eng. J. Med., 216:297, 1987. The blood cells were irradiated with UVA in an extracorporeal apparatus. The treated blood cells were returned to the body, leading to a response of the immune system against the tumor cells. The mechanism of the tumor cell damage was considered to be due to cross-linking of DNA by means of 8-MOP.
It has previously been assumed that the biological effects of psoralens are associated with their ability to bind covalently and cross-link DNA. However, Yurkow et al., J. Biol. Chem., 262 (18):8439-8442, 1987, disclose that a psoralen receptor was found in cytoplasmic and plasma membrane fractions of HeLa cells following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This cellular protein exhibits specific affinity for the psoralen compounds and becomes photoalkylated by these compounds. Yurkow et al further disclose that psoralen receptors in HeLa cells are a protein having a molecular mass of approximately 22,000 daltons. Binding of photoactivated psoralen to its receptor actually alters the proliferation and differentiation states of different cell types. Thus, the psoralens do not serve as general chemical cross-linkers but as very specific receptor activating ligands which activate the receptor only after photoactivation.
Additional evidence of psoralens not necessarily interacting directly with DNA is reported by Laskin et al., Proc. Nat. Acad. Sci. USA, 82: 6158-6162, 1985. Specific, saturable, high-affinity binding sites for 8-MOP have been identified on HeLa cells, and specific binding on other cell lines has also been found for 8-MOP.